Molecular dynamics simulation of structural evolution in crystalline and amorphous CuZr alloys upon ultrafast laser irradiation

A promising route for manufacturing emergent metamaterials is the use of ultrafast laser pulses in complex alloy processing. Laser-induced structural transformations in Zr-based alloys for crystalline and glassy states are investigated here. The ultrafast thermomechanical response is compared between relevant stable crystalline structures ${\mathrm{B}}_{2}\text{\ensuremath{-}}{\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, $\mathrm{C}{11}_{b}\text{\ensuremath{-}}{\mathrm{Cu}}_{33.3}{\mathrm{Zr}}_{66.7}$ and the amorphous structures $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{50}{\mathrm{Zr}}_{50}$, $\ensuremath{\alpha}\text{\ensuremath{-}}{\mathrm{Cu}}_{33.3}{\mathrm{Zr}}_{66.7}$. The subsurface modification resulting from ultrafast laser irradiation is investigated by a hybrid simulation to capture the phenomenon occurring at a picosecond time scale. This combines a two temperature model and molecular dynamics approaches to simulate laser matter interaction at the mesoscale. Our results indicate that the involved structural dynamics strongly depend on the initial atomic composition and phase structure. In particular, a martensite phase transition is unveiled for ${\mathrm{B}}_{2}$ crystalline alloy, and defects are induced in the irradiated $\mathrm{C}{11}_{b}$ phase, whereas the amorphous state of photoexcited metallic glasses remains remarkably preserved.